Piston



Jan. 12, 1937. DEBELACK 2,067,314

I PISTON Filed April 2, 1956 Fig.1 Fig.5

l i l i 55 Fig. 1 shows one embodiment, the left half of Strongly affected bi-metallically, wheas the 55 Patented Jan. 12, 1937 UNITED STATES PATENT OFFICE Claims.

This invention relates to pistons, especially for internal combustion engines, in which the shell comprises two metals having different coefficients of heat expansion united in such manner as to 5 produce a bi-metallic effect, accompanied by alterations in curvature so that the shell of the piston becomes accommodated to the expansion of the cylinder; that is to say, the bi-metallic action can be so adjusted that the bearing surface of the piston has the same expansion as the cylinder. For special purposes, the expansion could even be rendered negative.

The metal inserts which are employed to produce the bi-metallic action and which have a different coeflicient of expansion from the shell, are usually provided, above and below, in the .skirt of the piston, and, for reasons of cheaper production, inserts of the same metal are employed in both places, being arranged at the same distance from the wall of the skirt.

However, when such a piston is in operation it is found that, in accordance with the described constructional design, a greater degree of expansion occurs in the upper portion, where the piston rings are located, than lower down, by

reason of the higher working temperature prevailing in the upper portion. No alteration is obtained by doubly splitting the piston at the top alone (a measure that is known to facilitate the bi-metallic action of the piston wall). In order to find at least a partial remedy, the piston had to be tapered, and therefore allowed increased play at the top, especially when the skirt was split on one side only, or left solid.

An object of the present invention is to produce a more powerful bi-metallic action in the upper piston portion, where the piston rings are disposed, than lower down the skirt.

Acgrding to the invention, and taking into accounhthe higher working temperature in the upper pistonporgon, the upper and lower inserts are difierent in arrangement or manufacture. For example, the upper insert strips may be located nearer the periphery tthe outer wall of the piston) than the lower ones. Alternatively, for producing the same efiect. the upperfinsg -ts the figure representing an axial section of the piston, and the right half being a side elevation.

Fig. 2 shows, on the left, a cross section along II of Fig. 1, and, on the right, a cross section along II-II of the same figure. 5

Fig. 3 represents a second embodiment, in axial section on the left, and in side elevation on the right.

Fig. 4 shows, on the left, a cross section along IIIIII of Fig. 3, and, on the right, a cross sec- 10 tion along IV-IV of the same figure.

Fig. 5 represents two corresponding cross sections of another embodiment, the arrangement of the upper insert being shown on the left, and that of the lower one on the right. 15

Fig. 6 represents two corresponding sections of a fourth embodiment, the upper insert being shown on the left, and the lower oneon the right. i

In the first embodiment (Figs. 1 and 2) the 20 gudgeon-pin bosses 2 project, on both sides, from the shell 1 into the interior of the piston. The shell I is provided with a longitudinal slit 5, extending up and A own, and with an upper longitudinal slit 6. e upper and lower inserts 3 and 25 4, are arranged in such a manner that the upper insert 3 is brought nearer to the outer periphery of the piston Wall, than the lower one 4. By this means the bi-metallic action is more powerful above than below. 30

The piston illustrated by Figs. 3 and 4 is devoid of longitudinal slits. It has struts 1 located on the bosses 8. Over the greater portion of its perimeter, the head ll] of the piston is separated from the shell I by a slit 9. The upper insert 35 ring II is also, in this case, located nearer to the outer wall of the piston shell than is the lower one l2, so that a more powerful bi-metallic effeet is produced above than below.

The described arrangements, in which similar 4 materials are employed for the upper and lower inserts, and the increased bi-metallic action is obtained by approaching the upper insert closer to the outer perimeter of the piston skirt, provides the further advantage that, in consequence 45 of the unconditionally uniform shape of the inmaybe composed of a metal having a coefficient sort strips (as the result of the sectional form),

of expansiomwhichdifiers more from that of the piston skirt than does the metal of the lower inserts, in which case the spacing in relation to the wall of the piston is or may be the samefor both upper and lower inserts.

Typical embodiments of the invention are illustrated on the accompanying drawing.

a progressive bi-metallic elfect occurs, since the insert strips are cast-in eccentrically in relation to the peripheiq of the piston. Consequently, the bi-metallic effectis-rnqre powerful in the middle than at the ends.

By this means it is possiblFtaeet rid of the socalled abrasion corners", which may be more middle portions of the piston skirt, that is at the ends of the bi-metallic strip, have a weaker effect. Experiments have shown that the bi-metallic effect is produced with extraordinary precision, and even an unintentional deeper seating of the inserts, in casting in the shell, is noticeable in its expansion.

The term abrasion corners denotes the places where the piston usually abrades, that is, the lateral ends of the upper bearing surface, since it is known that high specific expansion of the skirt, owing to the heat generated in running, is accompanied by distortion due to the still hotter r piston head, which is attached to the skirt at the guided parts again situated nearer to the periphery of the piston skirt than are the lower inserts l4.

The same applies to the fourth embodiment (Fig. 6) in which the upper inserts i5 and the lower inserts l6 are solely arranged, on the outside, in external longitudinal recesses H formed by the special design of the piston shell l; but can also be guided on the inside (l9) if desired. In the parts 20 of the shell, which cover the recesses, the upper inserts are located nearer the external periphery of the shell than is the case with the lower ones, so that, in this case again,

' the more powerful bi-metallic effect occurs at the top.

According as the bearing surfaces of the piston are split or solid, the skirt must be circular, in the former case, and of oval cross section in the latter, so as to leave room for the inserted material on the bearing surface which, in consequence of the bi-metallic action, now expands in the lateral direction only.

I clain1:

1. A skirted piston having in its skirt upper and lower metal inserts differing as to coeflicient of expansion from the metal of the piston and affording greater bi-metallic action of the upper skirt portion than the lower skirt portion.

2. A skirted piston having in its skirt upper and lower metal inserts differing as to coefficient of expansion from the metal of the piston and from one another thereby to afford greater bimetallic action of the upper skirt portion than the lower skirt portion.

3. A piston according to claim 2, the upper and lower inserts being similarly spaced from the outer periphery of the skirt.

4. A skirted piston having in its skirt upper and lower metal inserts differing similarly as to coefficient of expansion from the metal of the piston, said upper insert being located nearer to the outer periphery of the skirt than the lower insert thereby to afford greater bi-metallic action of the upper skirt portion than the lower skirt portion.

5. A piston according to claim 4, the inserts being disposed eccentrically in relation to the periphery of the piston.

AUGUST DEBELACK. 

